1. Field of the Invention
This invention relates to probes for probe card assemblies.
2. Brief Description of the Prior Art
Probe assemblies are well known in probe card technology for checking integrated circuit, usually on a semiconductor wafer prior to scribing. Such probe assemblies usually contain a plurality of probes of electrically conductive material connected to a probe card, each probe usually having an electrically conductive body to which is connected an electrically conductive metal member in the form of a thin needle shape with a bent tip. The needles are designed to contact the various pads on the unscribed chips formed on the wafer with the bent tip and then to transmit thereto and receive therefrom electrical signals to determine operability of the chips on the wafer prior to further processing of the chips thereon, such as scribing, packaging and the like. This procedure eliminates further operation on faulty chips to provide the obvious economic advantages derived therefrom.
In order to perform the above noted tests, it is necessary that the probe assembly, which contains a sufficient number of probes thereon to contact anywhere from a portion of the pads on a single chip to all of the pads on the chip, be placed in contact with such pads. It is necessary that all of the probes contact their respective pads at substantially the same time and with substantially the same pressure. This is necessary because, if the probe tips are at different vertical positions relative to the pads with which they are associated, different forces are applied to the pads, depending upon the initial positions of the probe tips. This difference in force causes a variation in contact resistance with possible mistest of the chip and can even cause punch through of the pads. In addition, due to this problem of differences in vertical positioning of the probe tips, often some of the probes do not contact the chip surface or the pads thereon at all. It is desirable that the needle tips be within a range of about one mil from the first to touch to the last to touch. In addition, in view of the very small dimensions involved in chip and pad size, very small positioning errors can cause the probe tips to completely miss a pad during the testing operation. It is therefore apparent that the probe assemblies must be checked out to insure accurate positioning of each probe member along the plane of the chip surface as well as in a direction normal to the plane of the chip surface to be certain that precise contact with the pads is being made and at the proper pressure.
In the prior art, the positioning of mispositioned probes was corrected by taking a small hook or prod and bending on the probe needle. This type of needle adjustment was very imprecise and awkward. It was not only necessary to adjust the needle tip precisely, but also necessary that the adjustment be maintained. The needles, which are formed of electrically conductive materials, such as tungsten or beryllium copper, preferably have some spring action therein and have a tendency to return to their original position, this property being commonly known as metal memory. This problem of metal memory results in the requirement for continual rebending of the probes to keep them planar. In addition, the bending of the thin probe needle caused premature fatigue due to the stress at the location of the bend. It is therefore readily apparent that a simpler and more accurate method of adjusting the position of probe needles would be highly desirable in the present state of the art.